Using the Census mod and my server's demographics, the break out of 791 monks. 75% of monks are Panderians. 12% blood elves, and then everything else. Undead monks are the highest of evereything else with 6%.

Alliance side of the same server is pretty much the same tale, out of 2511 monks. 68% are Panderians, 15% Humans and then everything else. Nelfs are the highest of everything else with 6%

Rarest seems to be Troll Horde-side. Haven't met any as far as i can recall, seen of every other races tough. Hell one of my guild's main tank is a Tauren monk, wich are prolly the oddest to look at, specially when using RSK. They don't really seem physically fit or flexible enough for the task, but at the same time if a fat panda-man can do it...